Independent Channel Control in Coherent Optics

The present disclosure generally relates to optical transmitters and more particularly to default transmit power behavior for optical transceivers.

In the realm of optical communications, coherent optics technology is commonly used for high-capacity data transmission. This technology leverages modulation of the amplitude, phase, and polarization of light to encode information, allowing for the transmission of data at rates of 100 gigabits per second and beyond. Standards such as 400GBASE-ZR and OpenZR+ define the requirements and specifications for interoperable 400 Gbps optical devices. These standards are sometimes referred to as just 400ZR and 400ZR+, or variants like 400G-ZR and 400G-ZR+. 400ZR and 400ZR+ transceivers utilize 8 parallel lanes of PAM4 modulation to achieve aggregate data rates up to 400 Gbps on a single wavelength. However, higher or lower data rates are used by some coherent optics technologies, such as 100 Gbps or 800 Gbps.

Coherent optics are commonly employed in various applications, including long-haul transmissions, metro networks, and data center interconnects, due to their ability to efficiently utilize bandwidth and manage complex modulation schemes.

Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the disclosure is provided below, followed by a more detailed description with reference to the drawings.

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide an understanding of various embodiments of the inventive subject matter. It will be evident, however, to those skilled in the art, that embodiments of the inventive subject matter may be practiced without these specific details. In general, well-known instruction instances, structures, and techniques are not necessarily shown in detail.

Multiplexing techniques are used by coherent optical devices to increase the amount of data that can be transmitted over a single optical fiber, such as data from multiple clients. These techniques include wavelength division multiplexing (WDM) and its derivatives, which enable multiple data channels to share the same fiber by operating at the same wavelength. The management of these channels is important to network reliability and efficiency, as it involves the dynamic enabling and disabling of channels to perform maintenance, manage network resources, or respond to network conditions without disrupting the entire communication system.

However, in some cases, the default behavior of coherent optical devices in managing multiple multiplexed data channels may give rise to undesired effects. For example, in the default operational behavior of some coherent optics systems, when a data channel is disabled (often referred to as the channel being in an “admin down” state) the shared laser source associated with that channel is typically turned off. This action may be the result of a software command such as “set interface et-< > disable”, or another command to administratively disable a channel in a muxponder mode of the device, being executed in the system software managing the coherent optical device. As a consequence of disabling the laser, all channels that are multiplexed and share the same laser source and wavelength are inadvertently affected, leading to a complete shutdown of traffic across those channels. Typically, the remote device at the receiving end of the communication link will detect that it has stopped receiving the laser, and will eventually determine that the link has been terminated, e.g., based on a timeout counter. The remote device will categorize this event a “local fault” condition, thereby closing each data channel that was using the optical link (e.g., the same optical medium, such as a fiber optic cable). Each terminated channel will also result in a “remote fault” signal being asserted across the optical link to the local device where the laser has been disabled. The local device will receive the “remote fault” signals and, in response, terminate each data channel using the optical link.

This can result in significant network disruptions, especially in systems where multiple data channels are tightly integrated and rely on a single optical source for their operation. Thus, the inability to selectively disable a single channel without impacting the others is a notable limitation in such systems. Furthermore, disabling a laser carrying multiple data channels results in a complex sequence of signals being sent back and forth between the local and remote devices, further complicating and extending the process and introducing further data traffic into the optical link, thereby potentially increasing communication overhead and latency.

Examples described herein attempt to address one or more of these limitations of coherent optical devices by providing techniques for independent channel control in coherent optics systems. Some examples may attempt to address one or more technical problems related to optical communications, such as the inability to selectively and independently disable individual data channels being carried on the same optical source, and/or the unnecessary communication overhead and latency introduced by locally disabling a local optical source, thereby requiring the remote device to time out, disable multiple channels, and transmit remove fault signals for each disabled channel.

Some protocols have been proposed to handle independent control of individual data channels in coherent optics systems. For example, version 5.2 of the CMIS (Common Management Interface Specification) standard provides a specification for management interfaces of pluggable optical modules, and may enable some multiplexed optical channels transmitted between CMIS 5.2-compliant optical devices to be selectively disabled. However, these protocols require that both the local device (where the transmitting laser or other optical source is located) and the remote device (receiving the optical signal) implement the protocol or standard. Many devices currently deployed in optical networks do not implement these protocols; thus, for an optical network to benefit from these techniques, all devices on the network must be modified to implement them.

In contrast, examples described herein can be used to selectively and independently control individual data channels encoded in multiplexed signals received by a wide array of remote devices, including currently-deployed conventional optical devices. By leveraging existing standards, protocols, and behaviors of optical devices currently on the market and deployed in optical networks, independent and efficient data channel control can be implemented using examples described herein, without requiring existing network equipment to be modified or replaced. Techniques described herein can potentially be applied to a wide range of devices within the field of optical communications, including those that utilize coherent optics such as routers, switches, transponders, and optical line systems. These devices are often used in infrastructure that manages data transmission over long distances and between data centers, leveraging the advanced capabilities of coherent optics to maximize bandwidth and signal integrity. Additionally, some examples described herein are also applicable to normal optical devices, such as various forms of optical networking equipment.

shows a block diagram of an optical communication system. The optical communication systemincludes a first optical communication deviceand a second optical communication devicecommunicating with each other over an optical link. The first optical communication devicemay also be referred to herein as the local device or the transmitting device. The second optical communication devicemay also be referred to herein as the remote device or the receiving device.

In some examples, a network management system (shown as NMS) may be included in the optical communication systemto provide a management interface for a network administrator. An NMS is a set of software tools that enable an IT professional to monitor, control, and manage the entire lifecycle of a network infrastructure. An NMS can be used to manage both hardware (such as switches, routers, servers, and other network devices) and software (such as applications, services, and operating systems) components of the network. The NMScan be used to manage at least the first optical communication device, for example, by communicating with the first optical communication deviceover a communication link or network.

The first optical communication deviceincludes a controller, a first channelprovided by a first data interface, one or more additional channelsprovided by one or more respective additional data interfaces, and an optics module. The optics moduleincludes a multiplexerand an optical transmitter. The optical transmitterincludes an optical source. The controllerand data interfaces can be considered part of the system hardware and/or software of the first optical communication device, as distinct from the optics module. For example, each data interface can be implemented in the first optical communication deviceby medium access control (MAC) hardware, electrical signal multiplexing hardware (such as a probabilistic constellation shaping (PCS) module), and a 100 Gbit/second 2-lane electrical interface such as a 100GAUI-2 interface. The optics moduleis configured to communicate with the 100GAUI-2 interfaces of the various data interfaces of the system. Each data channel is therefore associated with the MAC of its data interface at the first optical communication device. (As used herein, MAC refers to the components (hardware and/or software) used to implement the MAC layer functionality of a given data interface.)

The second optical communication devicealso includes an optics moduleand a controller, as well as a first data interface receiving the first channeland one or more additional data interfaces receiving the one or more additional channels. The optics moduleincludes an optical receiverand a demultiplexer. As in the first optical communication device, the controllerand data interfaces can be considered part of the system hardware and/or software of the second optical communication device, as distinct from the optics module. As in the first optical communication device, each data interface can be implemented in the second optical communication deviceby medium access control (MAC) hardware, electrical signal multiplexing hardware (such as a probabilistic constellation shaping (PCS) module), and a 100GAUI-2 interface. The optics moduleis configured to communicate with the 100GAUI-2 interfaces of the various data interfaces of the system. Each data channel is therefore associated with the MAC of its data interface at the second optical communication device.

The optical linkcan be a single optical medium, such as a fiber optic cable, configured to carry an optical signal transmitted by the optical sourceto be received by the second optical communication device.

It will be appreciated that the first channelmay be any data channel processed by the optics moduleor optics module, and is not intended to be limited to a specific channel of a multi-channel system. Thus, the techniques described herein are equally applicable to any of the additional channelsas well as the first channel. The first channelcan be any arbitrarily selected channel of the system.

In operation, the first channeland additional channelsare received by the multiplexerof the optics module. The multiplexergenerates a multiplexed signalencoding the first channeland the one or more additional channels. The multiplexerprovides the multiplexed signalto the optical transmitter, which uses the optical sourceto transmit the multiplexed signalas an optical signal over the optical linkto a remote device, in this case the second optical communication device.

In some examples, the multiplexeris configured to support a 100G, 400G, or 800G coherent optics interface for transmitting the multiplexed signalover the optical link. The multiplexed signal, when transmitted over the optical linkby the optical transmitter, may therefore be a 100G, 400G, or 800G optical multiplexed signal. The techniques described herein may be applied more generally to any ethernet client signal encapsulated or multiplexed within an optical container, including any future optical multiplexed communication specifications.

In some examples, the optical transmitteris a coherent optical transmitter, and the optical sourceis a coherent optical source, such as a tunable laser configured to adjust a wavelength of the multiplexed signalwhen transmitting the multiplexed signalover the optical link. In other examples, a regular (non-coherent) optical source may be used instead.

The second optical communication devicereceives the optical signal from the optical linkat an optical receiver. The receiver provides the received signal to a demultiplexer. The demultiplexerdemultiplexes the multiplexed signalinto its constituent channels: the first channeland the one or more additional channels.

The controllerof the first optical communication deviceis configured to perform independent control of the data channels (e.g., first channeland the one or more additional channels) without disabling the optical source. When one of the data channels needs to be disabled, the controlleris able to disable the single identified data channel without disabling the optical source, by asserting a remote fault over a dedicated data channel, thereby allowing the remaining channels being encoded on the multiplexed signalto continue being transmitted over the optical linkwithout interruption.

shows operations of an example method for independent control of the data channels performed by the first optical communication device.shows additional operations of a second method performed by the second optical communication device. It will be appreciated that the methods shown inandcan form a single method performed by the optical communication systemin some cases.

illustrates an example methodof independently controlling data channels of an optical multiplexed signal. Whereas the operations of methodare described as being performed by the optical communication systemof, and specifically by the first optical communication device, it will be appreciated that one or more of the operations of methodcan be performed by other suitable devices and/or systems.

Although the example methoddepicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method. In other examples, different components of an example device or system that implements the methodmay perform functions at substantially the same time or in a specific sequence.

According to some examples, the methodincludes the first optical communication devicetransmitting the multiplexed signal, encoding the first channeland one or more additional channels, to the second optical communication deviceover the optical linkat operation.

According to some examples, the methodincludes the first optical communication devicereceiving a disable signalidentifying the first channelat operation. The disable signalis intended to assert that the identified channel (in this example, the first channel) needs to be disabled. In some examples, the disable signalis transmitted to the first optical communication deviceover a communication link or communication network (such as an ethernet network), for example, by the NMS. In some examples, the generation of the disable signalis internal to the first optical communication device: for example, the disable signalcan be generated by a logical process executed by the controller.

In some examples, the disable signalis generated in response to, or causes the generation of, a remote fault signal internal to the first optical communication device. For example, the disable signalreceived by the controllercan be triggered by a system or host of the first optical communication devicedetecting a local fault or remote fault notification in the data stream of the first channelbeing received by the first optical communication devicefrom a source internal or external to the first optical communication device. In some examples, the disable signalresults in the generation of a local fault or remote fault notification being generated and inserted into the data stream of the first channelat the first optical communication device, prior to the processing of the first channelby the multiplexer. In some examples, the disable signalis a local fault or remote fault signal present in the data stream of the first channel.

In response to receiving the disable signal, the subsequent operationsthroughare performed.

According to some examples, the methodincludes the optical transmitterof the first optical communication devicetransmitting a remote fault signal on the first channelof the multiplexed signal, to the second optical communication deviceat operation. A remote fault signal is a notification sent from one network device to another to indicate that a fault or error condition has been detected on the transmitting side of a link. The remote fault signal is used to inform the receiving device of the issue, allowing it to take appropriate action, such as disabling the affected link or rerouting traffic to maintain network integrity. In the context of optical communication, optical communication devices are configured to assert (e.g., transmit) and receive remote fault signals according to standardized formats and protocols.

In some examples, the controllercauses the first data interface to generate the remote fault signal. For example, the controller, in response to receiving the disable signal, can control the MAC hardware of the first data interface to generate and assert the remote fault signal. The remote fault signal is propagated to the optics module(e.g., by being multiplexed by the PCS module and propagated to the optics modulevia the 100GAUI-2 interface). The multiplexergenerates the multiplexed signalto incorporate the remote fault signal. The optical transmitterthen transmits the multiplexed signal, incorporating the remote fault signal, over the optical link.

In some examples, the first data interface may not be configured to generate the remote fault signal on command. Thus, in some cases, the controllermay instead control the MAC hardware of the first data interface to simulate a local fault. The simulated local fault is processed by the MAC hardware to result in the generation of the remote fault signal, which is asserted and propagated as described above.

According to some examples, the methodincludes the first optical communication devicedisabling the first channelat operation. Unlike existing optical multiplexing techniques, when the first channelis disabled in operation, the optical sourcecontinues to operate. The disable signalis processed by the controllerto disable the first channelwithout disabling the optical source, such that the optical sourceis maintained in an active state after the first channelis disabled. In some examples, the first channelcan be disabled by the controllerreconfiguring the data interfaces of the multiplexersuch that only the additional channelare configured as inputs to the multiplexer.

By using existing standards and protocols for formatting and asserting the remote fault signal, compatibility with existing network devices can be improved or maximized. Thus, the remote fault signal can be configured to be processed a remote device (e.g., second optical communication device) without the remote device implementing the CMIS 5.2 standard. Instead, the remote device can respond as intended to the remote fault signal in accordance with one or more standards, specifications, protocols, or behaviors predating the CMIS 5.2 standard.

In some examples, asserting the remote fault signal at operationcan be performed before, or concurrently with, disabling the first channelat operation.

According to some examples, the methodincludes the multiplexerof the first optical communication devicegenerating a modified multiplexed signal at operation. The modified multiplexed signal encodes the additional channelsbut not the first channel. The controllercan reconfigured the inputs of the multiplexersuch that the multiplexercontinues to generate a multiplexed signal, but the signal is now modified relative to the original multiplexed signalby the exclusion of the first channel.

According to some examples, the methodincludes the optical transmitterof the first optical communication devicetransmitting the modified multiplexed signal to the second optical communication deviceover the optical linkat operation. Because the second optical communication devicehas been notified to disable the first channelby the remote fault signal, the second optical communication deviceshould now be configured to receive and process the modified multiplexed signal, such that the demultiplexercan decode the modified multiplexed signal to extract the additional channels.

In some examples, the methodcan include additional operations not shown in the flowchart of. In some cases, if all of the additional channelsare disabled by the first optical communication deviceaccording to the same operations used to disable the first channel, the first optical communication devicemay respond by disabling the optical source(e.g., the transmit laser) to conserve power. Thus, for example, if the controllerdetermines that all data channels (e.g., all additional channels) using the optical sourcehave been disabled, the controllercan control the optical transmitterto disable the optical source.

Methodhas been described with respect to operations performed by the first optical communication device. A complementary second method, performed by the second optical communication device, is described below with reference to.

illustrates an example methodof independently controlling data channels of an optical multiplexed signal. Whereas the operations of methodare described as being performed by the optical communication systemof, and specifically by the second optical communication device, it will be appreciated that one or more of the operations of methodcan be performed by other suitable devices and/or systems. As described above, in some cases methodcan be combined with methodto form a single method performed by the optical communication system.

Although the example methoddepicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method. In other examples, different components of an example device or system that implements the methodmay perform functions at substantially the same time or in a specific sequence.

According to some examples, the methodincludes the second optical communication devicereceiving the remote fault signal at operation. As described above, the remote fault signal is received over the first channelof the multiplexed signal. In some examples, as described above, the remote fault signal is carried on the first channelof the multiplexed signal, which is demultiplexed by demultiplexer. The data of the first channeldecoded from the multiplexed signalis forwarded to a first data interface of the second optical communication deviceconfigured to receive the first channel. The system logic (e.g., controller) of the second optical communication devicethen processes the remote fault signal received on the first channel. In some examples, this processing proceeds in accordance with existing protocols and standards (e.g., not the CMIS 5.2 standard).

According to some examples, the methodincludes the second optical communication devicedisabling the first channelat operation. The controllerof the second optical communication deviceidentifies that the remote fault signal has been received over the first channel. The controllercan then disable the first channel, e.g., by reconfiguring the outputs of the demultiplexerto include only the additional channels. The MAC of the first data interface of the second optical communication device, associated with the first channel, can be disabled, thereby bringing down the network interface used by the first channel.

According to some examples, the methodincludes the second optical communication devicecontinuing to maintain the additional channelsat operation. The multiplexer, as reconfigured at operation, is now configured to decode only the additional channelsfrom the received optical signal (e.g., the modified multiplexed signal as described above).

As described above, the remote fault signal is configured by the first optical communication deviceto be processed by the second optical communication devicewithout using the CMIS 5.2 standard. Thus, the second optical communication devicecan be an optical communication device that does not implement the CMIS 5.2 standard. Instead, the second optical communication devicecan process the remote fault signal in accordance with a standard, protocol, specification, or behavior predating the CMIS 5.2 standard. This means that the methodcan be performed by a wide range of optical communication devices currently deployed in optical networks.

As used herein, the terms “controller” and “logic” may be used to refer to one or more hardware components of an optical communication device, such as an optical transceiver. A 100G, 400G, or 800G optical transceiver module contains logic devices to handle the transmit and receive functions, control interfaces, and monitoring capabilities required by the corresponding optical interface specification. In some examples, one or more components of the controller and/or logic may be configured by firmware or other software. In various examples, the controller or logic of an optical transceiver may include one or more components performing various logical and/or processing functions of the optical communication device. A microcontroller or state machine logic may be used to govern the overall operation of the optical transceiver. The microcontroller or state machine may boot up on transceiver module power up, initialize internal components, and implement control loops for functions like transmit power regulation. One or more serializer/deserializer (SerDes) devices may be used to convert between high-speed serial data and parallel interfaces. A transmit SerDes may be used to serialize the input parallel data into a fast serial stream. A receive SerDes may be used to deserialize the incoming serial data into parallel words. A digital signal processor (DSP) may be used to provide flexibility in processing and/or conditioning the high-speed serial data signals. A DSP may provide advanced modulation, pre-emphasis, equalization, framing, and error checking capabilities. One or more analog-to-digital and/or digital-to-analog converters (ADC/DAC) may be used to enable monitoring and control of laser drivers, photodiode inputs, and/or other analog signals. Optical source driver circuitry of the optical transmittermay be used to modulate the output of the optical source(e.g., a tunable transmit laser) based on input serial data. Receiver circuitry may be used to amplify and digitize an incoming photodiode signal.

In view of the disclosure above, various examples are set forth below. It should be noted that one or more features of an example, taken in isolation or combination, should be considered within the disclosure of this application.

Examples described herein may thereby provide various techniques for independent channel control in coherent and non-coherent optical communication systems.

The following are example embodiments:

Example 1 is an optical communication device comprising: a first data interface providing a first channel; one or more additional data interfaces providing one or more additional channels; a multiplexer configured to generate a multiplexed signal encoding the first channel and the one or more additional channels; an optical transmitter configured to transmit the multiplexed signal over an optical link to a remote device; and a controller configured to: receive a disable signal identifying the first channel; and in response to receiving the disable signal: cause the optical transmitter to transmit a remote fault signal to the remote device on the first channel of the multiplexed signal; disable the first channel; cause the multiplexer to generate a modified multiplexed signal encoding the one or more additional channels and not the first channel; and cause the optical transmitter to transmit the modified multiplexed signal to the remote device over the optical link.